Since an inorganic glass has excellent general properties such as excellent transparency and low optical anisotropy, the inorganic glass has been widely used in many fields as a transparent material. However, the inorganic glass has drawbacks such that it is heavy and easily broken, and has bad productivity when producing a product by molding and processing. As a result, a transparent organic polymer material (optical resin) has been used as a material in place of the inorganic glass. As the optical component obtained from such an optical resin, there are exemplified, for example, a plastic lens such as a spectacle lens for vision correction or a camera lens of a digital camera and the like. The optical components have been put to practical use and have come into use. In particular, for the purpose of use in a spectacle lens for vision correction, the plastic lens is lightweight and hardly broken, and can be tinted for granting great fashionability, as compared to the lens made of an inorganic glass. Making good use of such merits, the plastic lens has been widely used.
In the past, a crosslinking type resin obtained by casting polymerization of diethylene glycol bisallylcarbonate (hereinafter referred to as DAC) as an optical resin used for a spectacle lens under heating has been put to practical use. It has merits such that transparency and heat resistance are excellent, and the chromatic aberration is low (Abbe number is high). Due to such merits, it has been used the most for a general-purpose plastic spectacle lens for vision correction. However, there are problems such that wearing comfort and fashionability are worsened and the like since the central or edge thickness of the plastic lens becomes large because of the low refractive index (nd=1.50). Therefore, a resin for a plastic lens with a high refractive index capable of solving these problems has been demanded and developed accordingly.
During such a trend, since polythiourethane containing a sulfur atom obtained by casting polymerization of a diisocyanate compound with a polythiol compound is excellent in its transparency and impact resistance, while attaining a high refractive index (nd=1.6 to 1.7), and having relatively high abbe number and the like. By achieving such highly superior characteristics, polythiourethane has been used for the purpose of a high-quality plastic spectacle lens for vision correction in which the thickness is thin and its weight is light.
On the other hand, in a trend to pursue an optical resin having a much higher refractive index, there have been proposed several resins such as a transparent resin obtained by polymerization of a compound having an episulfide group in Patent Documents 1 and 2, a resin obtained by polymerization of a metal-containing compound such as Se in Patent Documents 3 and 4 or the like. However, the transparent resin obtained by polymerization of a compound having an episulfide group has a problem in mechanical properties, while the resin obtained by polymerization of a Se-containing metal compound has a problem in safety. Therefore, they have been demanded for further improvement. In recent years, there has been demanded an optical resin having required general properties (transparency, thermal properties, mechanical properties and the like) as a plastic lens, while attaining a much higher refractive index (nd) exceeding 1.7. The development of such an optical resin has been made.
[Patent Document 1] Japanese Patent Laid-Open No. 1997-110979
[Patent Document 2] Japanese Patent Laid-Open No. 1999-322930
[Patent Document 3] Japanese Patent Laid-Open No. 1999-140046
[Patent Document 4] Japanese Patent Laid-Open No. 2001-296402